1. Field of the Invention
The present invention relates to a vulcanized rubber molded product obtained by sulfur crosslinkage (vulcanization) and a method of producing the same and in particular to a vulcanized rubber molded product that is a foamed product obtained by continuously crosslinking (vulcanization)/foaming a rubber composition containing ethylene/α-olefin/non-conjugated polyene copolymer rubber etc. by a vulcanizing device such as a heated air vulcanizing bath (HAV), an ultra-high frequency vulcanizing device (UHF) etc., which is excellent in design, excellent in properties such as mechanical strength properties (tensile strength at break, tensile elongation at break), compression set resistance, abrasion resistance etc., and suitable for applications to automobile weather strips, glass run channels, opening trims, hoses etc., and a method of producing the same.
2. Description of the Related Art
Ethylene/α-olefin/non-conjugated polyene copolymer rubber such as ethylene/propylene/diene copolymer (EPDM) etc. is generally excellent in weatherability, heat resistance and ozone resistance, and is used for example in applications to automobiles, specifically vulcanized rubber products such as glass run channel products, window frame products or hose products.
The glass run channel products and window frame products are used for the purpose of protection against rain, wind and sound, and are important sealing parts. For increasing the duration of automobiles and for making maintenance free, there is a need for further improvements in sealing performance and long-term duration of the sealing performance. In respect of the hose products, there is a need for further improvements in heat resistance and sealing performance.
These properties are required as functions of the products, but the design of the vulcanized rubber products is also important. In the present specification, the “design” of the vulcanized rubber products refers to design depending on the surface smoothness, shape retention stability etc. of mainly the vulcanized rubber molded products (foamed products, non-foamed products).
The weather strip products are seen upon getting into or getting off an automobile, and thus their design exerts a significant influence on the image of the automobile itself.
When the vulcanized rubber product is a foamed product, its design is related closely to the state of foamed cells. When the foamed cells push up the surface of the vulcanized rubber product, the surface of the product becomes uneven to deteriorate its design. On the other hand, a vulcanized rubber product having the cells in broken state is not preferable because water permeates through the surface to deteriorate the functions thereof as a sealing product.
As a method of solving these problems, a method which involves surface treatment of a vulcanizable molded product (non-vulcanized rubber) consisting of ethylene/α-olefin copolymer rubber by coating the surface of the molded product with a treatment liquid containing a xanthogenate for accelerating vulcanization reaction and then vulcanizing the non-vulcanized rubber to give a vulcanized rubber molded product (non-foamed product) and a method which involves surface treatment of a vulcanizable, foaming molded product (non-vulcanized, non-foamed rubber) consisting of ethylene/α-olefin copolymer rubber by coating the surface of the molded product with the above treatment liquid and then vulcanizing and foaming the non-vulcanized, non-foamed rubber to give a vulcanized rubber molded product (foamed product) are disclosed in JP-A No. 4-202237 (page 2, upper right column to page 3, upper left column, and page 7, upper right column)
The vulcanized rubber molded product obtained by this conventional surface treatment method is excellent in design, but the chemical odor of the xanthogenate is strong, and it is troublesome to remove the chemical odor. As the method of coating the surface of the non-vulcanized rubber with the above treatment liquid, a dipping method using a coating bath is presented, but in this method where the non-vulcanized rubber is passed through the coating bath, the rubber surface is marred or the rubber molded product is deformed, and the rubber molded product in such state is converted into a vulcanized rubber product, which may result in deterioration of the design of the product. When the non-vulcanized rubber is molded at a lower molding speed, the rubber moves in a zigzag direction in a vulcanizing bath and entangled or bent in the chamber, which may result in problems such as failure to give an excellent vulcanized rubber product.
When the automobile weather strip product is divided roughly depending on the site where it is used, the weather strip has 3 constitutions, that is, one layer consisting of sponge rubber, two layers of sponge rubber/solid rubber, and three layers of sponge rubber/solid rubber/metal. The “sponge” refers to a foamed product, while the “solid” means a non-foamed product. The foamed product includes a product called slightly foamed solid.
The sponge rubber and solid rubber in these constitutions are different from each other in respect of performance required thereof, and are thus generally often different from each other in respect of the composition of starting materials. Accordingly, the sponge rubber and solid rubber show a different rate of crosslinkage at the molding temperature used, and thus one rubber tends to be excessively crosslinked while the other rubber tends to be poorly crosslinked. As a result, the product consisting of the 2 or 3 layers described above can be poor in interfacial adhesion between the sponge rubber and solid rubber, to easily cause defects such as interfacial separation.
For the sponge rubber in such a state as to give a sponge product by vulcanization reaction accompanied by foaming reaction, the time in which the maximum vulcanization reaction is generally reached is almost identical with the time in which the maximum foaming reaction is reached. When this balance is lost or the vulcanization reaction proceeds at a relatively higher rate than the foaming reaction, the surface smoothness of the sponge rubber product is improved and the design of the product is improved. However, such materials may scorch during molding to fail to give a product and are thus not practical.
Conventionally, when vulcanized rubber products having extremely excellent surface smoothness are to be obtained, many problems described above occur, and thus vulcanized rubber molded products (e.g. extruded sponge rubber, extruded solid rubber) having excellent surface smoothness have not been obtained.
Excellent mechanical strength properties and abrasion resistance are required of weather strip products and hose products. The weather strip products are desired to be resistant to abrasion with an automobile door and glass and resistant to abrasion with clothes in getting into or getting off an automobile. The hose products are required to be abrasion-resistant in order to prevent damage caused by abrasion among the hoses or between the hose and other products. It is known that resistance to such abrasion, or abrasion resistance, can be improved by increasing the density of crosslinkage by blending larger amounts of a crosslinking agent (vulcanizing agent), a vulcanizing accelerator and a crosslinking assistant. However, the tensile elongation and tensile strength have the optimum value respectively, and when tensile elongation is determined to be increased by the composition of starting materials, tensile strength is decreased, while when tensile strength is determined to be higher, tensile elongation is decreased. Accordingly, the design of rubber compositions achieving both tensile elongation and tensile strength is extremely difficult.
Under such circumstances, there is a need for a vulcanized rubber molded product which is a foamed product (sponge), has surface smoothness equal to or higher than that of a non-foamed product (solid) as a vulcanized rubber molded product, has excellent mechanical strength properties (tensile strength at break, tensile elongation at break etc.), and has compression set resistance and abrasion resistance as well as a method of producing the same, and there is also need for a vulcanized rubber molded product which is a non-foamed product (solid), is superior in surface smoothness to a conventional non-foamed vulcanized rubber molded product and has excellent compression set resistance, mechanical strength properties (tensile strength at break, tensile elongation at break etc.) and abrasion resistance as well as a method of producing the same.